Selective Separation of Arsenic(III) and (V) Ions with Ferric Complex of Chelating Ion-Exchange Resin

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Abstract
Trace levels of aqueous arsenic(III) and (V) ions were adsorbed selectively onto the ferric complex of a chelating resin, Uniselec UR-10. The adsorption was markedly dependent upon the pH of the aqueous phase. The distribution ratio and the specific adsorption capacity of arsenic(III) were 23,000 and 0.47 mmole/g, respectively, at the optimum pH for the adsorption, 9.2. The corresponding values of arsenic(V) were 22,000 and 0.53 mmole/g at the optimum pH 5.5. In the column operation the adsorption of the arsenic ions was also dependent upon the flow velocity and the size of the resin particle. A velocity of 60 cm/hr and 100 to 200 mesh size afforded satisfactory results. Adsorbed arsenic was recovered quantitatively by eluting the resin with 2 N hydrochloric acid, where the complexed iron was also eluted. A trace level of arsenic in wastewater from a geothermal power plant was successfully separated in the presence of a large excess of diverse cations and anions. Trace arsenic in natural seawater was also successfully preconcentrated 100 to 200 times over the original level by adsorption onto the ferric resin followed by elution with hydrochloric acid.